The invention relates to an apparatus for stacking flat letters.
In letter-processing systems, it is often necessary to store letters temporarily between two processing cycles. For example, for coupling asynchronously-working systems or parts, storage apparatus are used. One letter-storing technique involves temporarily stacking the letters.
Normally, a stacker comprises a stationary separating mechanism and a stacking mechanism that can move in the stacking direction, the letters being stacked therebetween. The base of the letter stack is formed by a stacking surface. Two endless belts that circulate around rollers form a transport path that conveys the individually-arriving letters to the end of the stack.
Between the stacking mechanism and the letter-loading loading station, the two belts form a straight section of the transport path on which the belts run freely, i.e., they are not guided by rollers in that section. The length of this partial section of the transport path is dependent on the momentary position of the stacker mechanism during the stacking process. As the letter stack grows, this partial section is shortened proportionally. It reaches its maximum length if there is no letter stack and the stacking mechanism is located directly at the separating mechanism.
Given a comparable engineering outlay, the storage capacity achievable with this design is, in fact, greater than that attainable with imbricated storage, where the letters are squeezed one on top of the other, in imbricated form, between belts. However, when working with the above-described type of apparatus, problems arise when the straight partial section of the transport path reaches its maximum length. In such a case, the situation may arise that a plurality of letters are located on the partial section at the same time. If this occurs in a manner such that a thin letter is situated between two thick letters on the straight section, the thin letter is not securely held by the belts. If a plurality of letters are situated between two thick letters, it can happen that the thin ones shift over on top of each other, causing a jam in the transport path and an interruption in the operation of the system. An additional problem is that the free-running belts hang increasingly lower as the length of the partial section in the transport path increases. Both problems may lead to a maximum stacker length of one meter for the type of stacker apparatus described above.